542 Prof. A. B. Macallum. Acineta tuberosa : [Feb. 19, 



interfaces, though possibly to an extent different from that obtaining in the 

 case of the potassium salts, and, consequently/ some of the haloid chlorine 

 demonstrated as present may be united with them. 



IV. General Observations. 



The foregoing observations make it evident that surface tension controls 

 the distribution of potassium salts in the cytoplasm of Acineta, and that, 

 whenever the surface tension at a point changes, there results a redistribution 

 of the salts, which conforms to the altered conditions of surface tension. 

 The quantity of potassium so affected appears to be very great as compared 

 with the amount which is diffused throughout the cytoplasm. In fig. 3 the 

 surface films of the tentacles, and the interfacial surfaces between the 

 maternal and germinal cytoplasms, seem to hold by far the vast part of the 

 potassium in the organism. "What is the exact proportion so condensed, as 

 compared with that in the cytoplasm generally, cannot be determined, but 

 the very marked concentration in the surface films of the tentacles, and the 

 almost entire absence of a reaction for potassium in the cytoplasm elsewhere, 

 suggests that the degree of concentration greatly exceeds the value 

 C dc 



S = — -— -— ^ . — . As already pointed out, Lewis found that the condensa- 



tion of potassium on the surface of the droplets of hydrocarbon oil in a 

 M/20 (0 - 373 per cent.) solution of potassium chloride was 5 x 10~ s grm./cm. 2 , 

 or thirty times the value 1*7 x 10 -9 grm./cm. 2 , calculated from the 

 equation. In a solution of the concentration M/20, the hexanitrite reagent 

 would give a dense precipitate, and a precipitate is given* when the 

 concentration of potassium is as dilute as 0*00039 per cent., or M/10000 KC1. 

 It is obvious, then, that the concentration of potassium chloride in the 

 cytoplasm is below this value, while the concentration of the condensation in 

 the surface films of the tentacles must be much above it. 



The thickness of the layer of condensation in the films is probably not as 

 great as appears indicated in the preparations. The thickness depends in 

 part only on the diameter of the molecules forming the surface films. If the 

 molecules were those of water, they should have, according to Kundt and 

 Warburg, a diameter of 3'39 x 10 -8 cm., and a range of molecular attraction 

 equal to 6"78 x 10 -8 cm. If, further, the surface tension in the films were as 



* The precipitate is found at the bottom of the test-tube containing the mixture of the 

 solution and reagent, after it has been allowed to stand for some hours. The precipitate 

 is also similarly given when the potassium chloride is of the concentration M/20000 in a 

 mixture of the solution and reagent. Crystals of the precipitate may, however, be found 

 in a drop of the mixture examined under the microscope a few minutes after it is made. 

 (The mixture in these cases should consist almost wholly of the reagent.) 



